This invention relates generally to handshake procedures of modems. The invention more particularly relates to procedures for automatic interworking between different modems.
As modems having different capabilities, including higher transmission rates, have been developed, it has been a desire in the industry to maintain "backwards compatibility". Backwards compatibility ensures that the newer modems are able to communicate with the modems already in the field. It also enables modems with increased capabilities to reduce the use of their capabilities and/or their transmission rates should the line over which the modems are communicating be incapable of permitting full utilization of those capabilities.
In order to accommodate backwards compatibility between modems, industry standards governing the communication between modems have been proposed and adopted. A good recent example of such a standard is an EIA/TIA Draft Standard PN2330 (Apr. 9, 1991) entitled "Procedures for Automatic Interworking between Automode Modems and V.32bis, V.32, V.22bis, V.22, V.21, V.23, 212-type and 103-type Modems", which document is hereby incorporated by reference herein in its entirety. Document PN2330 is provided to assist manufactures in the design of modems which can interwork with a variety of other modems adhering to different modulation standards. The standard is based on techniques presented in the CCITT recommendation V.32 Annex A, which is also hereby incorporated by reference herein in its entirety. The standard specifies a procedure for a modem to automatically detect the modulation technique and data signaling rate of the modem with which it is connected. When incorporated into a new modem which has the capability of using multiple modulation techniques, the specified procedure allows for automatic interoperation. The modulation techniques and data signaling rates of CCITT Recommendations V.32bis, V.32, V.22bis, V.21, V.23, and 212-type and 103-type modems (all of which are hereby incorporated by reference herein in their entireties) are addressed in the standard. However, it is of significant note that the modulation techniques and data signaling rates of V.fast modems, the standards of which are just now being formulated, are not addressed in the EIA/TIA PN-2330 standard. In fact, it is expected by those skilled in the art that the V.fast modems will add significant complications to the procedures for automatic interworking and may require an entire reworking of the draft a standards.